ORVR systems, although not restricted to automotive vehicles, is particularly suitable for use therewith. A fuel tank can receive fuel through an inlet pipe which has an inlet stub, of a diameter which is dimensioned to build up a column of fuel when fuel is filled into the tank. Apparatus is provided to control the liquid level and vapor flow which includes a filling vent line of a diameter sufficiently large to provide venting during fuel being filled into the tank, and an operating vent line, of a dimension small with respect to the diameter of the filling vent line, as well as a multipath valve which has a valve operating element, for example a pin or a cam, which controls the valve operation. Both the filling vent line and the operating vent line are coupled to the multipath valve. The multipath valve has an outlet to lead vapors vented through the valve to a vapor receptor. The valve operating element, in dependence on whether a fuel fill nozzle is present or absent in the fuel inlet stub, is operable to shift a valve fluid path between a filling mode position, when the nozzle is present, and an operating mode position, for example for operation of the vehicle and after the filling is completed and the nozzle is absent. In the filling mode position, the filling vent line is open, and in communication with the outlet leading to the vapor receptor, while the operating vent line is blocked. In the operating mode position, that is, when the filling nozzle is absent, the operating vent line is open and in communication with the outlet from the valve and hence the vapor receptor, while the filling vent line is blocked. A pressure equalization duct, of a diameter small with respect to the diameter of the filling vent line, is coupled from an end of the filling stub, for communication with the vapor receptor.
This type of arrangement is portion of an on-board refueling vapor recovery (ORVR) system in order to permit vapors, arising upon filling a fuel tank of the vehicle, that is, filling the tank "on board", to be connected to the vapor receptor. Typically, the vapor receptor has an active carbon filter. In operation, the active carbon filter is flushed with fuel vapors operating the vehicle, which dissolve off residues of fuel from the filter and lead it to combustion in an internal combustion engine.
The system described is part of a "liquid seal" system in which a column of fuel liquid builds up in the inlet stub, to form what might be termed a liquid seal to prevent escape of fuel vapors via the inlet stub. To form such a liquid column, the inlet stub is formed with a comparatively narrow cross section. This narrow cross section, however, has the result that the liquid column, after the fuel filling operation is terminated, tends to remain in the inlet stub, unless special arrangements are made to provide for draining of the inlet stub after the fuel filling operation is terminated.
To provide for draining of the liquid column, it has previously been proposed to provide a vapor pressure equalization line, located at an upper end of the inlet stub and in communication with the fuel vapor receptor. Such a vapor pressure equalization line must be so constructed that escape of fuel into the vapor receptor is prevented through the pressure equalization line. To ensure that no fuel can reach the vapor receptor, additional elements were used, such as check valves and switching valves in the pressure equalization line; such additional elements and valves increase assembly and manufacturing costs and additional contribute to the complexity of the overall system.